1. Field of the Invention
This invention relates to a commutatorless motor of the half-wave driven type provided with switching means that is on-off controlled depending on the angular position of rotation of a permanent magnet rotor, and more particularly to a burn-out preventive circuit for use in such a commutatorless motor for limiting the supply of a large current to the drive windings of the motor when the rotor is locked against rotation, thereby preventing burn-out of the drive windings.
2. Description of the Prior Art
As one of the prior art methods for preventing burn-out of the drive windings of a commutatorless motor when its rotor is locked against rotation due to an externally imparted force, a current limiting method is most frequently employed and commonly known which utilizes the fact that heat is generated from the drive windings or from a thermistor due to a large current appearing in the event of locking of the rotor. However, the prior art method utilizing the generated heat for preventing burn-out of the drive windings of the motor has had the problem of a slow response. Also, such a preventive device has been difficult to design especially when the motor is of the heavy-loaded type since the value of current in a locked condition does not appreciably change from that supplied under normal operation.